Difference Between Nucleus and Nucleolus

Cell is the building block of all the living organisms. There are various components of a cell. Cell organelles are there to perform different functions, which are needed for the survival of a cell. Nucleus is the main and most important organelle of a eukaryotic cell.

What is Nucleus?

Nucleus is a membrane bound organelle found in almost every eukaryotic cell. (But there are some eukaryotic cells without nuclei. E.g.|: red blood cells) Nucleus is the largest organelle in animal cells. It is round shaped. This is one of the essential organelles in a cell. It is surrounded by two membranes, and this membrane structure is similar to the plasma membrane structure. This is also known as the nuclear envelop. The outer nuclear envelop joins with the rough endoplasmic reticulum and it may have ribosomes on it. Nuclear envelop is discontinuous, and these spaces are known as pores. They occupy proteins, which act as trans-membrane channels. Nuclear envelop separates the content inside the nucleus from the cytoplasm and other organelles. There is a viscous liquid inside the nucleus similar to the cytoplasm and this liquid is known as the nucleoplasm. Majority of the cells, genetic material is located inside nucleus. DNA molecules, which are responsible for controlling the cell and inheriting genes, are arranged into chromosomes inside the nucleus. During the nuclear division in the cell cycle, nucleus undergoes four phases as prophase, metaphase, anaphase and telophase. During these phases, nucleus of a cell undergoes changes, and ultimately divides into two (in mitosis) or four (in meiosis) daughter nuclei. During this process, chromosomes appear as chromatins.

During the interphase, where cell undergoes normal functions, nucleus is important for protein synthesis regulation. The genes in DNA are expressed (gene transcription) to produce mRNA. These mRNA travel through the nuclear pores to the cytoplasm where translation process takes place to produce proteins. As mentioned above, some cells do not have nuclei, whereas some cells have numerous nuclei. For example, human muscle cells are polynucleated. Moreover, there are some cells where the nucleus takes different shapes or divides into lobes. For example, white blood cells like neutrophils have multi-lobed nuclei.

What is Nucleolus?

Nucleolus is a structure found within the nucleus. This is an area where it is highly dense. It can be observed as three regions. They are fibrillar centers, dense fibrillar component and granular component. Nucleolus is not surrounded by a membrane. It is formed by DNA units, which are supposed to code for rRNA for ribosome production. Therefore, main function of nucleolus is to synthesize rRNA and produce ribosomes.

What is the difference between Nucleus and Nucleolus?

• Nucleolus is located within a nucleus.

• Therefore, nucleolus is a suborganelle, whereas nucleus is an organelle within a cell.

• Nucleus is a double membranous organelle whereas nucleolus doesn’t have any membrane.

• Nucleus is mainly responsible for producing mRNA and nucleolus is mainly responsible for producing rRNA.

• Main functions of the nucleus are to control the cellular activities and regulate gene expression. Main function of nucleolus is to produce ribosomes.